Topics in Conservation

This section details 20 conservation topics listed by order performed. Some topics are familiar and widely used, while some are new and innovative. In each topic, an effort is made to present a technical intervention specification. This specification is a work-frame or a general plan that has to be adjusted to each site's unique conditions and on site assessment.

Some topics are referred to in site reports where these skills were performed.

The Center intends to continue to detail and update the conservation topics in this section from all the information, feedbacks and experience received at this site and from new projects.

The main goal is to standardize the information of archaeological site conservation by creating specific and general skill manuals for all conversation works and heritage sites..

Stone Cleaning

Professional stone cleaning includes four important aspects that must be understood, accounted for and adjusted to prior to implementation. See complete report.

Survey, documentation and assessment of state of conservation

These are the first actions to be done on a site intended for conservation and development. Data gathering from these activities provides an initial assessment that takes into account the potential that exists in the site, the developer's expectation and the extent of conservation work needed on site. The survey and documentation detail the architectural style, uses and functions, quality of workmanship and materials and conservation status. Analysis of present conservation status identifies and characterizes the decay processes, the causes and reasons for decay and establishes an overall picture.

Preventive-Maintenance Conservation

The most efficient way to keep the site's stability is by performing a preventive- maintenance and runoff water management plan. Such actions require a survey of the site or structure after rains, during the change of seasons and after unusual events. Identification and assessment of conservation problems in their early stages and the administration of simple and efficient treatments will ensure the survival of the site in the most authentic state and will save costly, professional treatment. An example of this is the identification of a missing stone in the wall or standing water in the foundations which can cause destabilization. Preventive treatments for these situations will prevent damage to the wall or structure. A similar example is thick-rooted vegetation that infiltrates the wall's core.

The diagnosis and identification of runoff water damage is simple to identify and does not require a professional conservator for the first stages. Locating the problems in the initial stages is critical for the structure's survival.

The conservation plan

The conservation plan is a comprehensive plan that implements the results of the survey, documentation and assessment. The plan graphically illustrates the present state of conservation and the interventions required to stabilize the decay process. All previous interventions on the site, their failures and success must be documented. The plan should include both general and specific topics, discuss technical specifications for interventions justifying the techniques, materials and level of conservation chosen for the site. The plan must create a conservation pilot model that estimates the time and costs of the interventions and continually checks estimated costs versus actual project advancement. The conservation plan must be made by a senior conservator and include reconstruction, development and engineering appendixes, made by conservation professionals, if required.

Examples:
The City of David-Jerusalem
Ein Gedi Oasis
Tel Arad

Site reburial and protection

Archaeological sites, without sufficient resources for the professional conservation and an unclear budget as to future excavations and development, must be fully documented and reburied for a short or long period. This is despite opposition by the site's patrons who usually have good but unrealistic intentions. Nevertheless, the reburial requires the support and intervention of the site's archaeologists. The entire excavated area needs to be covered with geo-textile cloth (not nylon) before reburial. There is great significance in the ability to see the location of the structure by allowing the wall-tops, assuming they are treated and the rest of the walls properly reburied, to protrude above the surrounding earth level. In some instances, it is possible to install simple drainage system in order to divert runoff water from sensitive areas as part of the reburial program. This protection recreates the relatively stable conditions that the ruins had since their abandonment prior to excavations.

Structure conservation

Structure conservation refers to the conservation and stabilization of all the surviving elements that together make a building i.e. roof, flooring, door and window openings. Conservation of a structure in this rare state of conservation requires special attention to details such as wall re-pointing, protective plaster, roof repairs, foundation stabilization and vegetation/runoff water management. Such monuments also require constant inspection and maintenance. An abandoned structure has its own pace and process of decay and substantial damage can occur quickly and unexpectedly.

Examples: Shivta-the Governor's Residence.

Conservation during excavation

Archaeological sites with a long term excavation plan and a possibility of becoming a national park must employ a professional conservator/crew for SOS and on-going treatments from the initial stages of excavation. It is important to ensure a long-term budget for conservation alongside the excavation and development works. Simple stabilization works must be administered from the beginning of the excavation. Some of these works can be done by the archaeologists themselves after basic training from the site conservators. Works such as: vegetation and run-off water management, sand bag support to floating foundations, floors and unstable walls, Geo-textile covering and backfill to delicate plaster and mosaic floors, Feeble lime mortar stabilization to loose stones, wall-tops and wall plasters, temporary fencing of the site.

Examples: Maale Zin Fortress.

Wall conservation

Wall conservation stabilizes and conserves a wall of a structure that no longer functions as in its original state. Originally, the wall was designed as part of a structure and usually as a wall bearing a roof, well plastered, drained and maintained. In a ruined structure the wall now functions as a landscape statue and only hints to the fact that once stood a wall that played an important role in the original structure. An exposed wall must be treated from the top, sides and foundation in order to prevent rain water or roots penetrating into the core. In addition, the treatment involves replacing missing stone, strengthening the core with compatible materials, treating the wall foundations, diversion of runoff water, re-pointing and vegetation treatment in and around the wall.

See specification: conserving dressed and field stone walls, re-pointing, grouting.

Landscape conservation

Today, great importance is given to the landscape surrounding the site. There now is a trend to preserve the landscape as was during the functioning of the site. In addition, in order for a site to receive a World Heritage nomination, it must have a buffer zone limiting future development in the surroundings. Landscape conservation has poised an interesting challenge for conservation and public presentation of the site.

Example: Mount of Olives-Jerusalem.

Floor conservation

The specification for floor conservation must take into account the functions of the floor and the different layers of the floor's foundation. It is not enough to only consider the upper layer of the floor, the one visible to the eye. The floor tells the life story of the structure; from pre-construction to its abandonment and destruction. The materials which make up the floor and its layers, help to understand it and the structure. Architectural remains found on the floor hint to the architectural character of the structure, roof and walls. Moreover, the way the floor was built hints to the structure's functions, characteristics owner's status and to the destruction phase.

All floors are built on an infrastructure. The infrastructure is made up of numerous layers of either earth mortar and/or lime mortar with the addition of large and/or small flat stones. These layers provided the floor with stability and prevented fracturing, collapse or the sinking of parts of the upper layers. The upper layer, on top of the foundation, was exposed to everyday life and was made out of pressed ash and/or lime concrete or flooring with field stones, dressed stones or mosaics. The infrastructure method and top layer were determined by the stability and dampness of the earth, the physical use of the floor, the availability of the construction material and the fashion of the period.

Examples: Tel Afek

Reconstruction for conservation needs

In many cases architectural elements exposed on the site have important parts missing. If there is a risk of collapse, in many cases, the missing parts can be reconstructed in order to stabilize the structure.

The materials used in the reconstruction must be identical in character and strength to the surviving material's present state, especially, if they are in a state of decay or disintegration.

The following should be taken into consideration; the aesthetic ramifications and the affect of using new or different materials on the appearance and the ability to understand the architectural element itself

In the case of reconstruction for conservation needs in walls with exposed cores and missing stones, in unstable mosaics and plasters, and in defective vaults and domes, the need to fill-in the missing details in order to stabilize and save the structure surpasses the argument against too much intervention and aesthetics. Professional reconstruction work for conservation purposes take into account all the claims and components and provides, in the end, a solution that is acceptable to most of the critics.

Examples:
Mahmal (before/after)
Madras Ruins

Mosaic conservation

Infrastructure and decay processes are similar in all types of flooring but in terms of floor conservation, the mosaic floor holds the biggest challenge and requires a high level of expertise, professionalism and years of experience.

The mosaic floor, like many floors from the classical period, is usually built of the statumen layer made of a thick earth/lime mortar with large, flat stones.. On top of this was the rudus layer, a thinner layer comprised of lime mortar and small, flat stones. On top of this was the nucleus, a layer of course lime mortar. On top of this was a fine layer of lime and sand into which the tesserae (mosaic stones) were fixed.

Reconstruction for presentation purposes

The presentation of the site and its development is crucial to the visitor's understanding of the site. Site development necessitates in depth understanding of the sites and all its aspects.

Reconstruction for presentation purposes must be based on architectural and engineering plans that are based on the principals of conservation including:

In depth understanding of the site including period of construction, original plan and construction technology.

Documenting present conservation state which includes identification and analysis of the decay process.

Authenticity principal – reconstruction plans for presentation purposes must be faithful to the unique principles and elements which compose the site.

Minimal intervention principal- based on facts discovered onsite. No reconstruction shall be done without factual basis such as anastilosis – the returning fallen architectural elements to their original location. In many incidents of reconstruction for presentation purposes, the imagination is used in a manner that disregards the factual basis and hence, the minimal intervention principal is breached.

Compatible material – onsite structural intervention must be done with materials that are compatible with the original materials in terms of composition, strength, porousity and durability. This principal de facto prohibits the use of modern alternatives such as cement, concrete, iron or other adhesives as substitutes to the original materials.

Reversibility - each material used on the site, whether it is modern or original, must have the ability to be reversible, meaning that it can be disassembled or detached without causing harm to the site's original material.

Examples:
Masada plans
Masada quarry
Masada presentation

Plaster conservation

Great importance lies in the remains of exposed plaster on the site's walls. The removal of layers of earth that protected the plaster for hundred and thousands of years and their exposure to climatic conditions and visitors poses a great challenge to the conservator.

The composition of ancient plaster is determined by many interdependent factors: period, population, region, uses, climate, material availability, technological level and economic capability. A detailed analysis of all the plaster system in each site and site is fascinating and provides evidence to the site's functions and population. From the end of the Neolithic-Calcolihtic period thru the Ottoman period, nearly 10,000 years, similar plaster systems were in use, both in material and technique. The chapter on building mortars describes earth and lime mortar composition. Plaster, differing from mortar had to be applied with great attention. The quality and size grade of the components, the rules for application and drying were the crucial foundation, especially, in lime plaster systems.

The composition of the original plaster system

Vitruvius, in his book describes a detailed method of making and applying lime plaster in 4-5 layers. This method is completely different than the modern method of applying cement plasters. The main role of lime plaster was to isolate and protect the soft stone, the wall core made of earth and/or lime, and preventing moisture from entering the structure. In addition, it provided protection and isolation from the climate conditions which were far stronger than man's capabilities.

Site development

A wide perspective of site development

The planning and development of heritage sites into visitor parks is an important tool for raising public awareness to the issue of conservation. This deepens the visitor's understanding of the site and raises the appreciation of the conservator's work. In addition, it also demonstrates the importance of maintaining the site for today's visitor and for future generations.

Fresco conservation

The foundation of a fresco painting is a lime plaster system.

Lime plaster

The layers of lime plaster which served as a foundation and wall straightening were made from lime mixed with sand, coarse aggregates and flat pottery shreds or small stones. On top of these foundation layers, usually two to three in number and 15-20 mm. thick, was the top layer made of fine sand lime plaster tightly pressed and smoothed. This top layer which was the decorative layer was, usually, 10 mm. thick.

Fresco and Secco

Throughout history and specifically during the classical period, it was common to lay another delicate layer of plaster, made of lime and marble powder, on which painting decorations were applied using natural pigments diluted with water. When the painting was done on freshly laid plaster, within the first 24 hours of drying the plaster and painting were called fresco (fresh). When the painting was done after the first 24 hours drying period, the dry plaster and painting were called secco (dry). The secco technique required adding delicate glue to pigments and water.

The pigment was absorbed into the fresh plaster and became a part of the layer during the first, 24 hour, drying period. This technique provided the pigment (painting) the same durability as the plaster itself. Nevertheless, the painted plaster is delicate and fragile, and even during ancient times required roofing and protection.

Examples: Masada villa 8

Project management

Conservation project management must be efficient and professional. In most cases, the budget consists of a one-time investment. The conservation plans and work specifications must be adapted to the nature of the site and the intervention. Choosing the materials for the intervention and logistical and physical organization of the site must be done before the actual work begins.

Every type of work and intervention on the project must be classified, differentiated, time estimated and staffed with crews of professional conservators and general workers.

Implementing a work plan allows the follow up of estimate versus accomplishment and can pinpoint problems in the scope and nature of works. On going problems must be solved even if a reassessment of the original plan is required.

Earth blocks and plaster conservation

Earth in construction

The term of earth in construction refers to a wide variety of construction methods including mud bricks, rammed earth, earth plaster, earth core in stone walls cooking and storage installations, tunnels and below earth construction. Abandoned and un-maintained earth structures have a low chance to survive. This is the reason that although humans, starting from the prehistoric age, are known to have built with earth, not much evidence exist in the archeological field.